The object of the invention is an elastic suspension system provided with a shock absorber intended for the rear wheel of a motorcycle, in which the rear wheel is carried by a fork that is pivoted to the motorcycle frame for a rocking movement thereabout, and the shock absorber is pivotally connected by its upper end to the motorcycle frame, at a point located at a higher level than the pivot point for the fork, while by its lower end it is pivotally connected to a shock absorber-supporting bell crank that is fulcrumed onto the fork for a pivoting movement thereabout, and has one end of a guide arm articulatedly connected thereto, the opposite end of said arm being articulatedly connected to the motorcycle frame.
In prior art suspension systems of this kind, the motorcycle frame, the fork, the guide arm, and the arm of the shock absorber-supporting lever which is included between the said lever fulcrum about the fork and the pivotal connection of said bell crank to the guide arm, form an articulated quadrilateral presenting at least two intersecting sides. More particularly, in these known suspension systems, when the shock absorber-supporting lever is in the form of a two-armed lever, the shock absorber is pivotally connected to the arm of this lever which is remote from the motorcycle frame, while the guide arm is articulatedly connected by one end to the said lever arm which is near to the motorcycle frame, and by its opposite end it is articulatingly connected to the motorcycle frame, at a lower position than the pivot point for the fork. Similarly, when in the known suspension systems of the aforementioned kind the shock absorber-supporting lever is in the form of a one-armed lever, to which both the shock absorber and the guide arm are pivotally connected, the guide arm has its opposite end articulatedly connected to the motorcycle frame at a lower position than the pivot point for the fork. In both instances, therefore, the pivotal connections of the shock absorber and of the guide arm to the motorcycle frame are located respectively above and below the pivot point for the fork. Moreover, while the suspension system is performing its elastic movement, the guide arm operates as a link.
The known suspension systems of the aforementioned kind however have the drawback of a much reduced shock absorber stroke. Additionally, while the suspension system is performing its elastic movement, the shock absorber is angularly moved, to a considerable extent, about the point of its pivotal connection to the motorcycle frame, and is caused to project backwards, so that it would bump into the rear wheel, or would unacceptably limit the movement of the wheel, if it were located in the same vertical plane as the rear wheel itself. This is why in the known elastic suspension systems of the aforementioned kind it was not possible to provide only one shock absorber located in the same vertical plane as the rear wheel, but two shock absorbers needed to be provided, arranged at the respective sides of the rear wheel.
The object of the invention is to eliminate the aforementioned drawbacks, and to provide an elastic suspension system of the kind initially disclosed, in which a considerably increased shock absorber stroke is obtained, and in which the shock absorber is not substantially moved angularly owing to the elastic movement of the rear wheel, so that it does not interfere with this wheel, whereby it is possible to provide only one shock absorber, intermediately arranged in the same vertical plane as the rear wheel.
The invention resides in the feature that the guide arm, and the portion of the shock absorber-supporting bell crank which is included between the fulcrum of said bell crank and the point of its pivotal connection to the guide arm, and the portion of the fork which is included between the fulcrum of the shock absorber-supporting bell crank and the pivot point for the fork, and that section of the motorcycle frame which is included between the pivot point for the fork and the articulation for the guide arm, form an articulated quadrilateral with no intersecting sides.
According to one advantageous embodiment of the invention, the guide arm has one end pivotally connected to the motorcycle frame, at a higher position than the pivot point for the fork. The opposite end of the guide arm may be pivotally connected to the shock absorber-supporting bell crank at any point thereof, which however should be such as to determine the uplifting of the pivot point for the pivotal connection of the shock absorber to the shock absorber-supporting bell crank, whenever the fork rocks in the upward direction about the pivot point for its pivotal connection to the motorcycle frame, as a result of the elastic movement of the rear wheel.
In one possible way of carrying out the construction of the elastic suspension system according to the just disclosed embodiment, the shock absorber-supporting bell crank consists of a two-armed lever, and the lower end of the shock absorber is articulatedly connected to that arm of the shock absorber-supporting bell crank which is adjacent to the motorcycle frame, while the guide arm is articulatedly connected to that arm of the shock absorber-supporting bell crank which is remote from the motorcycle frame.
The spring means of the suspension system may be arranged in any desired manner, and may act on the fork either directly or indirectly, through any partof the articulated quadrilateral associated with the fork. Preferably, however, the spring means of the suspension system are combined in known manner with the shock absorber and, for example, consist of at least one helical spring arranged co-axially to the shock absorber.